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Issue link: https://guyharveymag.epubxp.com/i/53451
A sand tiger on the wreck of the Papoose, off North Carolina. Photo: Doug Perrine / SeaPics.com. Tagging sand tigers in Delaware Bay. Photo: Shara Teter, GHRI. (One note here: Sand tigers, while fairly docile in respect to humans, are quite savage with each other, and of all places, in the womb. If multiple embryos form in the uterus, one embryo will eat the others. In other shark species, an embryo might eat other unfertilized eggs, but in this case, the alpha-embryo shark eats its developing siblings prior to birth. Only sand tiger sharks are known to show this grizzly type of intrauterine cannibalism—another juicy tidbit to tell the school kids.) What all of this means from a conservation perspective is that sand tiger populations are in the precarious position of being one of the shark species least able to handle even modest fishing mortality. This fact has led to a cautious management approach by the U.S. National Marine Fisheries Service, which made sand tigers a prohibited species in 1997 and then in 2004 placed it on a list to be considered for further protection under the Endangered Species Act. In an effort to help fishery managers determine the best course of action, GHRI graduate student Shara Teter has been partnering with the research teams of Dr. Dewayne Fox of Delaware State University and Dr. Brad Wetherbee of the University of Rhode Island to better understand the overall biology of this species, including its migration patterns and precisely how it uses the water column. In one study, the scientific team has been employing special satellite tracking tags donated by Microwave Telemetry to elucidate details of the movements of the sharks from aggregation sites in Delaware Bay, where sand tigers congregate by the hundreds each spring and summer before moving out as water temperatures drop later in the year. The long-held assumption has been that these animals move south toward the Carolinas and Florida. However, this assumption has been arrived at indirectly from fishery data and landing reports. To directly verify this behavior and obtain more details of the migrations of individual animals, the GHRI and partners placed satellite tags on eight males and three females, over the course of the summer. While the majority of the sharks followed the suspected pattern of moving south at the end of the season, three sharks did not. They were all young females. This was quite unexpected. Instead of moving south, these females swam east off the continental shelf, which is raising a range of questions that need to be answered for better management of this species. Is this difference typical migratory behavior of the sexes? Do older females show the same eastwards migratory pattern? If so, why are the sexes separating? Why are the young females going east as the coastal waters cool and how long do they remain in offshore waters? Key to the discovery of this previously unknown behavior is that the researchers were able to get the satellite tags to stay on and continuously record the movements of sharks for three to four months, an uncommon feat in the satellite tag tracking business where the tags often pull out of the animal just days or weeks after the shark is set free. And, what about the males? The thinner-skinned sex buzzed off to warmer climates, going nearly directly south after leaving Delaware Bay in the late summer and early fall. Their detailed tracks show them staying on or close to the continental shelf during a four-month migration (see track map). Interestingly, the males seem to take a migration break once in North Carolina locales, where they just mill around for a while. (Perhaps they hang out on the wrecks, hoping for a scuba diver encounter they can use later to impress the females—It was huge, blowing bubbles, and swimming right at me!) Lots of questions still remain to be answered. How far south do the males typically go? What drives them south–food, warmer water, sex? When and how do they make their return migrations north to Delaware Bay and surrounding environs? How much overlap is there between habitat use by these sharks and commercial fishing efforts where they run the risk of becoming bycatch? As the GHRI and its partners continue their research, this knowledge will help tremendously to improve fisheries management and conservation efforts for this ecologically vulnerable shark.